But received wisdom of this ilk is being shattered by new findings suggesting that 'ex-sex' can, in some cases, be a good idea.
Divorced partners who have slipped up and fallen back into the marital bed report that sex with an ex can actually lessen the psychological distress caused by the break-up.
Sex with a former lover can ease the pain of the split, says new research conducted at the University of Arizona and published in the Journal of Social and Clinical Psychology
Findings found that most participants (82.5 per cent) remained in contact with their ex after the separation, and almost one-fifth (21.9 per cent) had sex.
Whether or not the ex-sex actually helped a partner get over the end of their marriage depended on how 'over' it they already were.
Partners who hadn't accepted the break-up found the intimate encounters actually helped lessen the pain of divorce.
We're always taught that sex with an ex is an emotional minefield, but new research suggests it could actually help partners having difficulty coming to terms with a break-up
Sex toy firm Lovehoney found that more women than men look back with longing on past relationships and admit to having had better sex with an ex than with their current partnerPsychologists believe that break-ups can leave us with attachment needs that go unfulfilled, and that sex with an ex helps to provide some sense of security, and at least partial fulfillment of those needs.
Sex toy firm Lovehoney found that more women than men look back with longing on past relationships and admit to having had better sex with an ex than with their current partner.
The survey of 1,100 adults found that 38 per cent of women said the best sex of their lives was in a previous relationship.
Sex and relationship expert Tracey Cox said this 'grass is greener' syndrome is not new.
Cox said many women benefited from having sex with their ex because it ultimately gave them 'closure' on the relationship.
Tracey Cox, sex expert, said: 'I still think it's dodgy ground if there's a lot of emotion involved - iif a much-loved partner who has left is interested in sex with you it sends of message of hope - and that could be false hope'
'Sometimes we need to go back to move forward, and revisiting the sexual side of the relationship can sometimes make us see very clearly that we've idealised it'Cox, who has her own range of sex toys with Lovehoney, warned women to wary before jumping into bed with their ex.
She said: 'But I still think it's dodgy ground if there's a lot of emotion involved. If a much-loved partner who has left is interested in sex with you it sends of message of hope - and that could be false hope.
'On their side it's a trip down sexual memory lane, on your side, it's make-up sex with a view of rekindling.
'If you're going to do it, make sure you go into it with a clear understanding of what it means to the other person.'
In the hit movie It's Complicated, Meryl Street and Alec Baldwin star as exes who start sleeping together years after they divorce.